This invention relates to modified elastomeric block copolymers. More particularly, this invention relates to modified block copolymers which are useful in blends with polyester molding compositions.
The use of unsaturated polyesters in thermosetting molding compositions is well known. Generally, these compositions comprise an unsaturated polyester, a vinyl monomer and a curing agent. The thermosetting resin composition may also comprise other additives such as fillers, reinforcing agents, anti-shrinking agents, thickeners and the like. The unsaturated polyester resin compositions generally exhibit excellent rigidity, heat resistance and electrical characteristics when used in thermosetting applications. Products prepared with unsaturated polyester molding compositions do not, however, generally exhibit good impact resistance or good surface characteristics. The poor surface characteristics are attributed to shrinkage during curing of the composition.
U.S. Pat. No. 4,329,438 teaches improved polyester molding compositions which contain a carboxylated derivative of a styrene-butadiene block copolymer. Specifically, the styrene-butadiene block copolymer is modified by grafting an unsaturated dicarboxylic acid or an unsaturated dicarboxylic acid derivative to the block copolymer. According to the disclosure, signficant improvement of blend properties including surface appearance are realized.
U.S. Pat. No. 4,851,474 teaches polyester resin compositions having improved impact resistance and surface characteristics wherein shrinkage is controlled by addition of a hydroxyl or carboxyl terminated conjugated diene polymer which has been hydrogenated and reacted with an unsaturated polyester. The product of the reaction was believed to have blocks of polyesters attached predominantly at the terminal carboxyl or hydroxyl sites. Coupling of the carboxyl terminated polymers is avoided.